#! /usr/bin/env python
# Copyright (c) 2009, 2010, 2011, 2012 Nicira, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at:
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


# A daemon to monitor attempts to create GRE-over-IPsec tunnels.
# Uses racoon and setkey to support the configuration.  Assumes that
# OVS has complete control over IPsec configuration for the box.

# xxx To-do:
#  - Doesn't actually check that Interface is connected to bridge
#  - If a certificate is badly formed, Racoon will refuse to start.  We
#    should do a better job of verifying certificates are valid before
#    adding an interface to racoon.conf.


import argparse
import glob
import os
import subprocess
import sys

import ovs.dirs
from ovs.db import error
from ovs.db import types
import ovs.util
import ovs.daemon
import ovs.db.idl
import ovs.unixctl
import ovs.unixctl.server
import ovs.vlog

vlog = ovs.vlog.Vlog("ovs-monitor-ipsec")
root_prefix = ''                # Prefix for absolute file names, for testing.
SETKEY = "/usr/sbin/setkey"
IP = "/sbin/ip"
exiting = False
IPSEC_MARK = "1"


def unixctl_exit(conn, unused_argv, unused_aux):
    global exiting
    exiting = True
    conn.reply(None)


# Class to configure the racoon daemon, which handles IKE negotiation
class Racoon:
    # Default locations for files
    conf_file = "/etc/racoon/racoon.conf"
    cert_dir = "/etc/racoon/certs"
    psk_file = "/etc/racoon/psk.txt"

    # Racoon configuration header we use for IKE
    conf_header = """# Configuration file generated by Open vSwitch
#
# Do not modify by hand!

path pre_shared_key "%s";
path certificate "%s";

"""

    # Racoon configuration footer we use for IKE
    conf_footer = """sainfo anonymous {
        pfs_group 2;
        lifetime time 1 hour;
        encryption_algorithm aes;
        authentication_algorithm hmac_sha1, hmac_md5;
        compression_algorithm deflate;
}

"""

    # Certificate entry template.
    cert_entry = """remote %s {
        exchange_mode main;
        nat_traversal on;
        ike_frag on;
        certificate_type x509 "%s" "%s";
        my_identifier asn1dn;
        peers_identifier asn1dn;
        peers_certfile x509 "%s";
        verify_identifier on;
        proposal {
                encryption_algorithm aes;
                hash_algorithm sha1;
                authentication_method rsasig;
                dh_group 2;
        }
}

"""

    # Pre-shared key template.
    psk_entry = """remote %s {
        exchange_mode main;
        nat_traversal on;
        proposal {
                encryption_algorithm aes;
                hash_algorithm sha1;
                authentication_method pre_shared_key;
                dh_group 2;
        }
}

"""

    def __init__(self):
        self.psk_hosts = {}
        self.cert_hosts = {}

        if not os.path.isdir(root_prefix + self.cert_dir):
            os.mkdir(self.cert_dir)

        # Clean out stale peer certs from previous runs
        for ovs_cert in glob.glob("%s%s/ovs-*.pem"
                                  % (root_prefix, self.cert_dir)):
            try:
                os.remove(ovs_cert)
            except OSError:
                vlog.warn("couldn't remove %s" % ovs_cert)

        # Replace racoon's conf file with our template
        self.commit()

    def reload(self):
        exitcode = subprocess.call([root_prefix + "/etc/init.d/racoon",
                                    "reload"])
        if exitcode != 0:
            # Racoon is finicky about its configuration file and will
            # refuse to start if it sees something it doesn't like
            # (e.g., a certificate file doesn't exist).  Try restarting
            # the process before giving up.
            vlog.warn("attempting to restart racoon")
            exitcode = subprocess.call([root_prefix + "/etc/init.d/racoon",
                                        "restart"])
            if exitcode != 0:
                vlog.warn("couldn't reload racoon")

    def commit(self):
        # Rewrite the Racoon configuration file
        conf_file = open(root_prefix + self.conf_file, 'w')
        conf_file.write(Racoon.conf_header % (self.psk_file, self.cert_dir))

        for host, vals in self.cert_hosts.iteritems():
            conf_file.write(Racoon.cert_entry % (host, vals["certificate"],
                    vals["private_key"], vals["peer_cert_file"]))

        for host in self.psk_hosts:
            conf_file.write(Racoon.psk_entry % host)

        conf_file.write(Racoon.conf_footer)
        conf_file.close()

        # Rewrite the pre-shared keys file; it must only be readable by root.
        orig_umask = os.umask(0077)
        psk_file = open(root_prefix + Racoon.psk_file, 'w')
        os.umask(orig_umask)

        psk_file.write("# Generated by Open vSwitch...do not modify by hand!")
        psk_file.write("\n\n")
        for host, vals in self.psk_hosts.iteritems():
            psk_file.write("%s   %s\n" % (host, vals["psk"]))
        psk_file.close()

        self.reload()

    def _add_psk(self, host, psk):
        if host in self.cert_hosts:
            raise error.Error("host %s already defined for cert" % host)

        self.psk_hosts[host] = psk
        self.commit()

    def _verify_certs(self, vals):
        # Racoon will refuse to start if the certificate files don't
        # exist, so verify that they're there.
        if not os.path.isfile(root_prefix + vals["certificate"]):
            raise error.Error("'certificate' file does not exist: %s"
                    % vals["certificate"])
        elif not os.path.isfile(root_prefix + vals["private_key"]):
            raise error.Error("'private_key' file does not exist: %s"
                    % vals["private_key"])

        # Racoon won't start if a given certificate or private key isn't
        # valid.  This is a weak test, but will detect the most flagrant
        # errors.
        if vals["peer_cert"].find("-----BEGIN CERTIFICATE-----") == -1:
            raise error.Error("'peer_cert' is not in valid PEM format")

        cert = open(root_prefix + vals["certificate"]).read()
        if cert.find("-----BEGIN CERTIFICATE-----") == -1:
            raise error.Error("'certificate' is not in valid PEM format")

        cert = open(root_prefix + vals["private_key"]).read()
        if cert.find("-----BEGIN RSA PRIVATE KEY-----") == -1:
            raise error.Error("'private_key' is not in valid PEM format")

    def _add_cert(self, host, vals):
        if host in self.psk_hosts:
            raise error.Error("host %s already defined for psk" % host)

        if vals["certificate"] == None:
            raise error.Error("'certificate' not defined for %s" % host)
        elif vals["private_key"] == None:
            # Assume the private key is stored in the same PEM file as
            # the certificate.  We make a copy of "vals" so that we don't
            # modify the original "vals", which would cause the script
            # to constantly think that the configuration has changed
            # in the database.
            vals = vals.copy()
            vals["private_key"] = vals["certificate"]

        self._verify_certs(vals)

        # The peer's certificate comes to us in PEM format as a string.
        # Write that string to a file for Racoon to use.
        f = open(root_prefix + vals["peer_cert_file"], "w")
        f.write(vals["peer_cert"])
        f.close()

        self.cert_hosts[host] = vals
        self.commit()

    def _del_cert(self, host):
        peer_cert_file = self.cert_hosts[host]["peer_cert_file"]
        del self.cert_hosts[host]
        self.commit()
        try:
            os.remove(root_prefix + peer_cert_file)
        except OSError:
            pass

    def add_entry(self, host, vals):
        if vals["peer_cert"]:
            self._add_cert(host, vals)
        elif vals["psk"]:
            self._add_psk(host, vals)

    def del_entry(self, host):
        if host in self.cert_hosts:
            self._del_cert(host)
        elif host in self.psk_hosts:
            del self.psk_hosts[host]
            self.commit()


# Class to configure IPsec on a system using racoon for IKE and setkey
# for maintaining the Security Association Database (SAD) and Security
# Policy Database (SPD).  Only policies for GRE are supported.
class IPsec:
    def __init__(self):
        self.sad_flush()
        self.spd_flush()
        self.racoon = Racoon()
        self.entries = []

    def call_setkey(self, cmds):
        try:
            p = subprocess.Popen([root_prefix + SETKEY, "-c"],
                                 stdin=subprocess.PIPE,
                                 stdout=subprocess.PIPE)
        except:
            vlog.err("could not call %s%s" % (root_prefix, SETKEY))
            sys.exit(1)

        # xxx It is safer to pass the string into the communicate()
        # xxx method, but it didn't work for slightly longer commands.
        # xxx An alternative may need to be found.
        p.stdin.write(cmds)
        return p.communicate()[0]

    def call_ip_xfrm(self, cmds):
        exitcode = subprocess.call([root_prefix + IP, "xfrm"] + cmds)
        if exitcode != 0:
            vlog.err("couldn't install IPsec policy that prevents "
                     "traffic from exiting unencrypted")

    def get_spi(self, local_ip, remote_ip, proto="esp"):
        # Run the setkey dump command to retrieve the SAD.  Then, parse
        # the output looking for SPI buried in the output.  Note that
        # multiple SAD entries can exist for the same "flow", since an
        # older entry could be in a "dying" state.
        spi_list = []
        host_line = "%s %s" % (local_ip, remote_ip)
        results = self.call_setkey("dump ;\n").split("\n")
        for i in range(len(results)):
            if results[i].strip() == host_line:
                # The SPI is in the line following the host pair
                spi_line = results[i + 1]
                if (spi_line[1:4] == proto):
                    spi = spi_line.split()[2]
                    spi_list.append(spi.split('(')[1].rstrip(')'))
        return spi_list

    def sad_flush(self):
        self.call_setkey("flush;\n")

    def sad_del(self, local_ip, remote_ip):
        # To delete all SAD entries, we should be able to use setkey's
        # "deleteall" command.  Unfortunately, it's fundamentally broken
        # on Linux and not documented as such.
        cmds = ""

        # Delete local_ip->remote_ip SAD entries
        spi_list = self.get_spi(local_ip, remote_ip)
        for spi in spi_list:
            cmds += "delete %s %s esp %s;\n" % (local_ip, remote_ip, spi)

        # Delete remote_ip->local_ip SAD entries
        spi_list = self.get_spi(remote_ip, local_ip)
        for spi in spi_list:
            cmds += "delete %s %s esp %s;\n" % (remote_ip, local_ip, spi)

        if cmds:
            self.call_setkey(cmds)

    def spd_flush(self):
        self.call_setkey("spdflush;\n")
        self.call_ip_xfrm(["policy", "add", "src", "0.0.0.0/0", "dst",
                           "0.0.0.0/0", "proto", "gre", "dir", "out",
                           "mark", IPSEC_MARK, "mask", IPSEC_MARK,
                           "action", "block", "priority", "4294967295"]);

    def spd_add(self, local_ip, remote_ip):
        cmds = ("spdadd %s %s gre -P out ipsec esp/transport//require;\n" %
                    (local_ip, remote_ip))
        cmds += ("spdadd %s %s gre -P in ipsec esp/transport//require;\n" %
                    (remote_ip, local_ip))
        self.call_setkey(cmds)

    def spd_del(self, local_ip, remote_ip):
        cmds = "spddelete %s %s gre -P out;\n" % (local_ip, remote_ip)
        cmds += "spddelete %s %s gre -P in;\n" % (remote_ip, local_ip)
        self.call_setkey(cmds)

    def add_entry(self, local_ip, remote_ip, vals):
        if remote_ip in self.entries:
            raise error.Error("host %s already configured for ipsec"
                              % remote_ip)

        self.racoon.add_entry(remote_ip, vals)
        self.spd_add(local_ip, remote_ip)

        self.entries.append(remote_ip)

    def del_entry(self, local_ip, remote_ip):
        if remote_ip in self.entries:
            self.racoon.del_entry(remote_ip)
            self.spd_del(local_ip, remote_ip)
            self.sad_del(local_ip, remote_ip)

            self.entries.remove(remote_ip)


def update_ipsec(ipsec, interfaces, new_interfaces):
    for name, vals in interfaces.iteritems():
        if name not in new_interfaces:
            ipsec.del_entry(vals["local_ip"], vals["remote_ip"])

    for name, vals in new_interfaces.iteritems():
        orig_vals = interfaces.get(name)
        if orig_vals:
            # Configuration for this host already exists.  Check if it's
            # changed.  We use set difference, since we want to ignore
            # any local additions to "orig_vals" that we've made
            # (e.g. the "peer_cert_file" key).
            if set(vals.items()) - set(orig_vals.items()):
                ipsec.del_entry(vals["local_ip"], vals["remote_ip"])
            else:
                continue

        try:
            ipsec.add_entry(vals["local_ip"], vals["remote_ip"], vals)
        except error.Error, msg:
            vlog.warn("skipping ipsec config for %s: %s" % (name, msg))


def get_ssl_cert(data):
    for ovs_rec in data["Open_vSwitch"].rows.itervalues():
        if ovs_rec.ssl:
            ssl = ovs_rec.ssl[0]
            if ssl.certificate and ssl.private_key:
                return (ssl.certificate, ssl.private_key)

    return None


def main():

    parser = argparse.ArgumentParser()
    parser.add_argument("database", metavar="DATABASE",
                        help="A socket on which ovsdb-server is listening.")
    parser.add_argument("--root-prefix", metavar="DIR",
                        help="Use DIR as alternate root directory"
                        " (for testing).")

    ovs.vlog.add_args(parser)
    ovs.daemon.add_args(parser)
    args = parser.parse_args()
    ovs.vlog.handle_args(args)
    ovs.daemon.handle_args(args)

    global root_prefix
    if args.root_prefix:
        root_prefix = args.root_prefix

    remote = args.database
    schema_helper = ovs.db.idl.SchemaHelper()
    schema_helper.register_columns("Interface", ["name", "type", "options"])
    schema_helper.register_columns("Open_vSwitch", ["ssl"])
    schema_helper.register_columns("SSL", ["certificate", "private_key"])
    idl = ovs.db.idl.Idl(remote, schema_helper)

    ipsec = IPsec()

    ovs.daemon.daemonize()

    ovs.unixctl.command_register("exit", "", 0, 0, unixctl_exit, None)
    error, unixctl_server = ovs.unixctl.server.UnixctlServer.create(None)
    if error:
        ovs.util.ovs_fatal(error, "could not create unixctl server", vlog)

    interfaces = {}
    seqno = idl.change_seqno    # Sequence number when we last processed the db
    while True:
        unixctl_server.run()
        if exiting:
            break

        idl.run()
        if seqno == idl.change_seqno:
            poller = ovs.poller.Poller()
            unixctl_server.wait(poller)
            idl.wait(poller)
            poller.block()
            continue
        seqno = idl.change_seqno

        ssl_cert = get_ssl_cert(idl.tables)

        new_interfaces = {}
        for rec in idl.tables["Interface"].rows.itervalues():
            if rec.type == "ipsec_gre":
                name = rec.name
                options = rec.options
                peer_cert_name = "ovs-%s.pem" % (options.get("remote_ip"))
                entry = {
                    "remote_ip": options.get("remote_ip"),
                    "local_ip": options.get("local_ip", "0.0.0.0/0"),
                    "certificate": options.get("certificate"),
                    "private_key": options.get("private_key"),
                    "use_ssl_cert": options.get("use_ssl_cert"),
                    "peer_cert": options.get("peer_cert"),
                    "peer_cert_file": Racoon.cert_dir + "/" + peer_cert_name,
                    "psk": options.get("psk")}

                if entry["peer_cert"] and entry["psk"]:
                    vlog.warn("both 'peer_cert' and 'psk' defined for %s"
                              % name)
                    continue
                elif not entry["peer_cert"] and not entry["psk"]:
                    vlog.warn("no 'peer_cert' or 'psk' defined for %s" % name)
                    continue

                # The "use_ssl_cert" option is deprecated and will
                # likely go away in the near future.
                if entry["use_ssl_cert"] == "true":
                    if not ssl_cert:
                        vlog.warn("no valid SSL entry for %s" % name)
                        continue

                    entry["certificate"] = ssl_cert[0]
                    entry["private_key"] = ssl_cert[1]

                new_interfaces[name] = entry

        if interfaces != new_interfaces:
            update_ipsec(ipsec, interfaces, new_interfaces)
            interfaces = new_interfaces

    unixctl_server.close()
    idl.close()


if __name__ == '__main__':
    try:
        main()
    except SystemExit:
        # Let system.exit() calls complete normally
        raise
    except:
        vlog.exception("traceback")
        sys.exit(ovs.daemon.RESTART_EXIT_CODE)
